Portable terminals such as portable telephones have become increasingly popular in recent years. Such portable terminals typically use a liquid crystal display device for an output display section. These portable terminals are frequently used outdoors, and therefore, are required to ensure stable operation over a wide temperature range. The lower limit of the guaranteed operating temperature range is set to an extremely low level such as about −30° C.
At low temperature, a liquid crystal display device is disadvantageous in that the frequency characteristics of the liquid crystal dielectric constant are degraded, causing the contrast at low temperature to become low. In more detail, referring to FIG. 3 showing an equivalent circuit for a unit pixel, the resistance component R of the liquid crystal material increases at low temperature, thus preventing the pixel electrode, with a liquid crystal capacitance Clc, from being sufficiently charged within a predetermined period of time. Consequently, a desired signal voltage cannot be written to the pixel, causing the contrast to become low.
This problem of low contrast at low temperature is notable particularly in a liquid crystal display device operated at a low voltage to reduce power consumption, in which a lower voltage is applied to the liquid crystal capacitance Clc. In order to overcome the problem described above, a higher voltage may be applied to the liquid crystal capacitance Clc; however, this approach produces another problem in that the output circuit of the data driver for driving the data lines requires a high current capacity, thus consuming more power and occupying a larger circuit area.
A selector drive system, employed in a color liquid crystal display device, is a well-known system that allows three color signals corresponding to three horizontally arranged colors to be time-sequentially sampled within one horizontal period and then written to the data lines in the display area, thus reducing the number of outputs of the data driver to one-third. In such a liquid crystal display device employing the selector drive system, three color signals are sequentially sampled within one horizontal period, and therefore, a shorter period of time is allocated, in particular, for the third sampled color. This problem is more noticeable at low temperature for the reasons described above. Thus, a desired signal voltage cannot be written to the pixel of the third sampled color. As a result, the contrast of the third sampled color becomes significantly low, causing a chromaticity shift (chromaticity deterioration).
In view of the above-described problem, it is an object of the present invention to provide a liquid crystal display device that increases the contrast characteristics at low temperature while still suppressing power consumption and that reduces a chromaticity shift if the selector drive system is employed; a method for driving such a liquid crystal display device; and a portable terminal having such a liquid crystal display device at an output display section.